MEASURING HUM IN A DIGITAL TV SIGNAL
First Claim
1. A method for measuring Hum in a digital television (DTV) signal comprising quadrature amplitude modulation (QAM) signals using a testing device for testing QAM signals on a cable television (CATV) network, the method comprising:
- a) receiving the DTV signal with the testing device, the testing device comprising a DTV receiver and a controller coupled thereto, the DTV receiver comprising a first QAM demodulator for demodulating a first QAM signal comprised in the DTV signal, wherein the DTV receiver further includes a plurality of automatic gain control (AGC) stages in a signal path of the first QAM signal, each AGC stage comprising an AGC register for storing a current AGC gain value of the respective AGC stage,b) sampling values stored in one of the AGC registers at a pre-defined sampling rate R that exceeds two times a Hum frequency to obtain a first sequence of AGC samples; and
,c) using the controller to store and analyze the first sequence of AGC samples, or at least a portion thereof, for evaluating Hum in the first QAM signal.
4 Assignments
0 Petitions
Accused Products
Abstract
The invention relates to a method for measuring Hum on a digital QAM carrier using a testing device for testing digital TV signals including a QAM demodulator therein, and to a testing device implementing the method. A controller is used to sample a register associated with a final AGC stage in a QAM demodulator, and to process the collected register values to obtain one or more Hum characteristics. In one embodiment, a circular buffer is used to collect aligned sequences of AGC samples that have a pre-determined feature of time-domain Hum at a specified position therein. The aligned AGC sequences are then correlated to assess causes of Hum.
-
Citations
19 Claims
-
1. A method for measuring Hum in a digital television (DTV) signal comprising quadrature amplitude modulation (QAM) signals using a testing device for testing QAM signals on a cable television (CATV) network, the method comprising:
-
a) receiving the DTV signal with the testing device, the testing device comprising a DTV receiver and a controller coupled thereto, the DTV receiver comprising a first QAM demodulator for demodulating a first QAM signal comprised in the DTV signal, wherein the DTV receiver further includes a plurality of automatic gain control (AGC) stages in a signal path of the first QAM signal, each AGC stage comprising an AGC register for storing a current AGC gain value of the respective AGC stage, b) sampling values stored in one of the AGC registers at a pre-defined sampling rate R that exceeds two times a Hum frequency to obtain a first sequence of AGC samples; and
,c) using the controller to store and analyze the first sequence of AGC samples, or at least a portion thereof, for evaluating Hum in the first QAM signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
-
-
14. A testing device for testing a digital television (DTV) signal on a cable television (CATV) network, comprising:
-
an input port for receiving the DTV signal; a DTV receiver comprising a first QAM demodulator for demodulating a first QAM signal comprised in the DTV signal, the DTV receiver further comprising a plurality of automatic gain control (AGC) stages in a signal path of the first QAM signal, wherein the plurality of AGC stages comprises a final AGC stage within the first QAM demodulator, and one or more preceding AGC stages, the final AGC stage comprising an AGC register for storing a current AGC gain value thereof; a controller coupled to the DTV receiver for tuning the DTV receiver to the first QAM channel and for sampling the content of the AGC register of the final AGC stage; and
,an output device coupled to the controller; wherein the controller is programmed to perform operations comprising; a) sampling values stored in the AGC register of the final AGC stage at a pre-defined sampling rate R that exceeds two times a Hum frequency to obtain a first sequence of AGC samples; and
,b) analyzing the first sequence of AGC samples to obtain one or more Hum characteristics; and
,c) providing the one or more Hum characteristics to the output device for storing therein or reporting to a user. - View Dependent Claims (15, 16, 17, 18, 19)
-
Specification